9.
POWER MODULES AND D50 TESTING
The power module houses one SCR and one diode per module, in a configuration
shown in Figure 5. Simple tests with an ohmmeter cannot conclusively show that
an SCR or a rectifier is good, but shorted SCR’s or open or shorted rectifiers can
be detected. Remove all wires connected to the power cube. Refer to Figure 5.
Using a Simpson 260 meter or equivalent, make the following measurements:
a)
With the meter between the “AC” and “+” terminals on POWER
MODULE # 1, the meter should read high ( several hundred K ohms )
when “AC” is either plus or minus in respect to the “+” terminal.
Repeat this step for POWER MODULE # 2.
b)
POWER MODULE #1 diodes can be checked by putting one lead on
the “-“ terminal. The other lead should be put on the “AC” terminal.
With the meter leads on the “AC” and “-“ terminals the Simpson on
the RX1 resistance scale, the meter should read between 5-15 ohms
when the “-“ terminal is positive in respect to the ‘AC” terminal. With
the meter voltage polarity reversed, the meter will read high. Going to
a higher meter resistance scale such as RX100 or RX10000 will
indicate a resistance greater than 100K ohms. Repeat this step for
POWER MODULE #2.
Replace the module if found to be faulty.
c)
Check D50 by connecting the plus lead of the meter to the anode of
D50 and the minus lead of the meter on the cathode of D50. Refer to
Figure 5. With the meter on the RX1 resistance scale, the meter should
read between 5-15 ohms. When the meter leads are reversed, the meter
should read high (on the RX10000 scale reading will be greater than
100k ohms).
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